docs: def add_log(self, group_name, field_name, log_string):
          """ Add a log the file.
          :param group_name: Global group name. Cave: No 'Analyses' is prepended.
          :param field_name: A field {group_name}/{field_name} will be written.
          :param log_string: content to be written.
          """
          self.assert_writeable()
          if group_name not in self.handle:
              self._add_group(group_name, {})
          sanitized_data = _sanitize_data_for_writing(log_string)
          self.handle[group_name].create_dataset(field_name, data=sanitized_data)